RTL SDR up-converter for HF use

I picked up a RTL SDR from amazon a while back for around 20 bucks. It works fine on VHF/UHF. I wanted to try it on HF. Typically these inexpensive devices can not go below about 25MHz. In order to listen in on some MF and HF stuff I decided to throw together a quick and dirty up converter.

With up-conversion I am basically shifting the lower HF frequencies into a range that the SDR dongle can see. In this case with a 7MHz base frequency into the up-converter, the SDR will see it as 32MHz.

https://www.amazon.com/RTL-SDR-Blog-RTL2832U-Software-Telescopic/dp/B011HVUEME/ref=sr_1_4?ie=UTF8&qid=1504202463&sr=8-4&keywords=rtl+sdr

Using what I had laying around, I found a 25MHz crystal so I made a crystal oscillator and buffer going into a double balanced mixer. This is all built into an Altoids container with a pigtail of RG-174 to go to the SDR reciever and a BNC for the antenna connection. The setup runs on a 9 volt battery.

Some images follow of the up converter below as well as a couple test videos of reception.

Transformers wound on binocular cores from science and surplus. -AC9LF

Oscillator and buffer circuit with 25Mhz crystal. -AC9LF

Double balanced mixer added with 9V connector. -AC9LF

I may change the oscillator to 40MHz because of harmonic mixing. For example at 50MHz which is double the 25Mhz crystal frequency the up conversion starts all over again. It would not work well at 10 meters.

I put a simple low pass RC filter at antenna end with the cut off at about 30Mhz the values were 22ohms and 220pF respectively. I might change this to a better LC type filter later. Initial testing seemed promising with a small ~2 foot antenna hooked up as you can see in the short video below.

This first video is of a couple AM stations on the up converter. 

This next video is of some SSB on 40 meters.

I may edit this with a schematic later. I don't have anything scratched down right now.

Crude up-converter doing its thing. -AC9LF

I used Cubic SDR and Ubuntu Mate for the PC side of things.

Edit: 10/09/2017 schematic below.

https://drive.google.com/file/d/0B-GeQSy2vlYfSjMxVUM4ZWYzUTQ/view?usp=sharing


SSB reception with magnetic loop antenna attached.